Expansion valve for air conditioning system with proportional solenoid

ABSTRACT

An expansion valve (10) for heat transfer systems such as an air conditioning system, includes a control element (20) for controlling the flow rate of working fluid through the valve. The control element has a stem member (28) and movable member (42) movable on the stem member. Openings (38) to an internal passage (30) in the stem member are regulated by positioning the movable member to achieve regulated flow rate of refrigerant material through the valve. The movable member of the control element is moved by a plunger (24) of a proportional solenoid (22). The proportional solenoid has a magnetic flux circuit including a low permeance isolation tube (62) surrounding the plunger, which enables removal of the coil (76) and frame (78) of the solenoid from the valve. The solenoid further includes a variable permeance flux washer (69) the flux through which varies with plunger position, which is disposed from a gap (82) which provides an area of magnetic saturation. The proportional solenoid produces force/displacement characteristics which enable precise control of the control element and accurate regulation of the refrigerant flow rate through the valve.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 08/161,000 filed on Dec. 3,1993, now U.S. Pat. No. 5,390,897, which is a divisional of U.S.application Ser. No. 07/961,567 filed Oct. 15, 1992, now U.S. Pat. No.5,295,656, which is a continuation-in-part of U.S. application Ser. No.07/951,259 filed Sep. 25, 1992, now U.S. Pat. No. 5,252,939, thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to heat transfer systems. Specifically thisinvention relates to an expansion valve for a vehicle air conditioningsystem.

BACKGROUND ART

Heat transfer systems, such as air conditioning systems and heat pumpsystems, are well known in the prior art. In such systems a workingfluid which can be any one of a number of refrigerant materials is usedto transfer heat from one region to another.

The working fluid typically passes through a system that includes anevaporator, a compressor, a condenser and an expansion device. Of coursethe system may also include other components such as an accumulator or areceiver/dryer.

In an air conditioning application the evaporator is positioned in thespace to be cooled and the condenser is positioned in the area to whichheat removed from the cooled space is transferred. Working fluid in thevapor state is pumped by the compressor into the condenser. In thecondenser the working fluid rejects heat and condenses to a liquid.

The liquid working fluid passes from the outlet of the condenser into anexpansion device. Expansion devices known in the prior art include fixedorifices, capillary tubes and expansion valves.

From the expansion device the working fluid flows to the evaporatorwherein it absorbs heat and undergoes a change of phase from liquid tovapor. The refrigerant vapor then flows back to the compressor to beginanother pass through the system.

The expansion device is an important element of the system. The amountof working fluid that passes through the expansion device is acontrolling factor in the amount of cooling that can be achieved.However, because the temperature of both the space being cooled and thespace to which heat transferred vary, the pressure and temperature ofthe liquid working fluid entering the expansion device also varies. Thisimpacts the cooling capabilities of the system and affects the flow ratethat must be obtained through the expansion device to achieve theoptimum cooling effect. In mobile systems such as those used as airconditioning or refrigeration systems on vehicles, the properties of theworking fluid delivered to the expansion device can vary widely.

Due to the variable operating conditions of vehicle heat transfersystems, fixed opening expansion devices such as orifices and capillarytubes are sometimes used to reduce cost but are not preferred. Instead,expansion valves that provide variable refrigerant flow rates are moredesirable.

Prior art expansion valves have traditionally controlled flow by passingthe fluid through an internal opening in the valve and employing amovable restricting body or other element in close proximity to theopening. Moving the restricting body closer to the opening reduces flow.Conversely, moving the restricting body away from the opening increasesflow through the valve.

In prior art expansion valves the position of the restricting body hasbeen controlled by an actuator. A common actuator is a diaphragm typewhich is mounted on the valve. The actuator opens or closes flow throughthe expansion valve in response to fluid pressure both inside the valveand from a control source.

The control source fluid pressure for moving the restricting body isdelivered from a sealed bulb which holds a carefully determined fluidcharge. The bulb is commonly mounted adjacent to the outlet line fromthe evaporator. When the temperature of the working fluid exiting thespace to be cooled begins to increase, the temperature of the bulb alsoincreases. As the pressure of the fluid inside the bulb increases itmoves the diaphragm and the blocking body inside the expansion valve toincrease the flow rate of working fluid to the evaporator. The increasedflow of working fluid provides more cooling and eventually thetemperature at the outlet of the evaporator drops. When this occurs thepressure inside the bulb falls, moving the diaphragm and the restrictingbody to reduce the flow rate of working fluid through the valve. Thecharge in the bulb is contrived to have a small amount of superheat inthe refrigerant leaving the evaporator.

A problem with this type of prior art actuator is that the expansiondevice is constantly seeking the optimum rate of flow. The response timerenders the expansion device unable to react properly to changingconditions. This is particularly a problem in vehicle applications wherechanges in cooling loads and variations in refrigerant properties arecommon. As a result, the accuracy of control is also less than optimum.

Others have previously used electrically controlled expansion valves tocontrol the flow of working fluid in a heat transfer system. Thesesystems typically use valves that are either fully open or fully closed.The valve is periodically opened and closed for controlled time periodsto achieve an overall average flow rate that is designed to handle theheat transfer load at the evaporator.

A significant problem with such pulse width modulated expansion valvesis that they must open and close very frequently. This causes rapid wearof the valve components. The opening and closing action also oftencauses "hammering" in the system. The vibration associated withhammering may cause fatigue and premature failure of the valve and theconnected tubing. It also makes accurate pressure measurementimpossible.

The control elements used in prior art expansion valves for controllingor regulating the flow of working fluid also have drawbacks. The valvesthat meter flow must be made to deal with the static and dynamicpressure effects created by the working fluid as it passes through thevalve. In some designs efforts are made to use the pressure of theworking fluid to develop balancing forces. These balancing forces enablemore precise movement of the restricting body or other control element.This is intended to enable more precise control of the flow rate.

The problem with attempts to design expansion valves that make use ofsuch balancing forces is that the forces vary substantially with thefluid conditions and the flow rate. As a result it has been difficult toproduce an expansion valve that provides accurate control of fluid flowover a wide range of operating conditions.

Thus there exists a need for an expansion valve for heat transfersystems that provides accurate flow control for the working fluid undera wide range of operating and flow conditions.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an expansion valvethat accurately controls the flow of working fluid therethrough.

It is a further object of the present invention to provide an expansionvalve that includes a control element that minimizes the influence offlow and pressure effects.

It is a further object of the present invention to provide an expansionvalve that includes a proportional solenoid actuator that accuratelycontrols flow through the control element.

It is a further object of the present invention to provide an expansionvalve that minimizes vibration and has a long useful life.

It is a further object of the present invention to provide an expansionvalve that has few moving parts, is economical to manufacture and isreadily repaired.

It is a further object of the present invention to provide an expansionvalve that can be operated with flow in either direction.

Further objects of the present invention will be made apparent in thefollowing Best Modes for Carrying Out Invention and the appended claims.

The foregoing objects are accomplished in the preferred embodiment ofthe invention by an expansion valve for controlling the flow ofrefrigerant material flowing to an evaporator of a heat transfer system,such as a vehicle air conditioning system. The valve has a body with aninlet for receiving liquid refrigerant material and an outlet fordelivering expanded refrigerant material.

The expansion valve includes a control element between the inlet and theoutlet for controlling the flow rate of refrigerant material through thevalve. The control element has a cylindrical stem member with aninternal passage. The stem member has a cylindrical outer surface. Theouter surface preferably includes a pair of opposed longitudinallyelongated openings.

The control element further includes a movable member mounted formovement on the outside of the stem member. The movable member ismovable through a range positions between a first position wherein thevalve is fully open and a second position wherein the valve is fullyclosed.

In a first embodiment, the control element is configured to be anormally closed element. However in other embodiments the valve may beconfigured to be normally open. The control element is not significantlyinfluenced by flow or pressure forces, and is thereby enabled to providean accurate rate of flow depending on the position of the movablemember. It also accomodates flow in either direction through theelement.

The movable member of the control element is positioned by aproportional solenoid actuator. The proportional solenoid actuator isconstructed with a novel low friction plunger as described in U.S.patent application Ser. No. 07/951,259, filed Sep. 25, 1992, now U.S.Pat. No. 5,252,939, the disclosure of which is incorporated herein byreference.

The proportional solenoid actuator also includes a novel removable coildesign that facilitates repair or replacement of the actuator. Thesolenoid actuator also includes a novel magnetic flux circuit thatincludes a low permeance, non-magnetic isolation tube in series with avariable permeance element. This construction provides a proportionalsolenoid that achieves accurate positioning of the movable member of thecontrol element in response to electrical signals delivered to theproportional solenoid actuator.

Accurately positioning the control element of the valve through movementof the proportional actuator, enables accurate flow control through theexpansion valve and precise control of the cooling effects of the systemin which the expansion valve is used.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of a first embodiment of the expansionvalve of the present invention.

FIG. 2 is a side view of a normally closed control element of theexpansion valve shown in FIG. 1.

FIG. 3 is a cross sectional side view of the control element shown inFIG. 2.

FIG. 4 is a side view of a normally open control element of analternative embodiment of the expansion valve of the present invention.

FIG. 5 is a cross sectional view of the control element shown in FIG. 4.

FIG. 6 is a cross sectional view of the proportional solenoid actuatorof the expansion valve shown in FIG. 1.

FIG. 7 is a schematic view of a heat transfer system incorporating theexpansion valve of the present invention.

BEST MODES FOR CARRYING OUT INVENTION

Referring now to the drawings and particularly to FIG. 1, there is showntherein a first embodiment of the expansion valve of the presentinvention generally indicated 10. The valve has a body 12. The body 12includes an inlet 14 for receiving liquid refrigerant working fluid. Thevalve also has an outlet 16 for delivering expanded working fluid to anevaporator or other exothermic heat exchanger.

The body 12 further includes a chamber 18. A control element 20 ispositioned in chamber 18. As later explained, fluid passing from inlet14 to outlet 16 of the valve is required to pass through the controlelement.

Valve 10 further includes a proportional solenoid 22. Solenoid 22includes a movable plunger element 24. Plunger element 24 is a lowfriction type plunger of the type described in co-pending U.S. patentapplication Ser. No. 07/951,259, filed Sep. 25, 1992, now U.S. Pat. No.5,252,939, the disclosure of which is incorporated herein by reference.As later described in detail, plunger element 24 is controlled to movedownward in response to electrical signals supplied to the proportionalsolenoid 22.

Body 12 of valve 10 further includes a return passage 26. Return passage26 provides a path for working fluid from the evaporator as it returnsto the compressor and the remainder of the system (see FIG. 7). Returnpassage 26 provides a convenient location for sensors for detecting thecharacter and properties of the refrigerant material leaving theevaporator. However, in other embodiments of the invention the expansionvalve need not include a return passage through body 12.

Control element 20 is shown in greater detail in FIGS. 2 and 3. Controlelement 20 has a stem member 28 that includes an internal passage 30.The stem member has a threaded lower portion 32 for attaching to asimilarly threaded opening in body 12 (not separately shown) which is influid communication with outlet 16. The stem member 28 also has a hexarea 34 to facilitate installation and removal of the control elementfrom the valve.

Stem member 28 includes a cylindrical outer surface 36. A pair ofopposed longitudinally elongated openings 38 extend on outer surface 36.Openings 38 are in fluid communication with internal passage 30 throughducts 40. Ducts 40 are similarly configured to openings 38.

Control element 20 further includes a movable member 42. Movable member42 has a cylindrical inner surface 44 that is slightly larger indiameter than outer surface 36 of stem member 28. As a result, movablemember is axially movable on stem member 28.

Movable member 42 includes an enlarged flange area 46. Flange area 46 isin abutting relation at its lower side with a compression spring 48 asshown in FIGS. 2 and 3. Compression spring 48 biases the movable memberupward as shown in the drawings.

The upper surface of flange area 46 supports a cap portion 50 of themovable member. Cap member 50 includes a open area 52 that enables it tomove downward on stem member 28 a significant distance without engaginga closed top area 54 of the stem member. Cap portion 50 also has arounded plunger engaging portion 56. Plunger engaging portion 56 ofmovable member 42 engages plunger 24 as shown in FIG. 1, as the movablemember is biased against the plunger by spring 48.

Movable member 42 further includes tapered peripheral surface 58.Peripheral surface 58 is tapered as shown in FIGS. 2 and 3 such that itis substantially thinner at a terminating edge 60.

As shown in FIGS. 2 and 3, spring 48 biases movable member 42 upward,and the peripheral surface 58 of the movable member covers openings 38in the outer surface of stem member 28 when no downward force is appliedby the plunger of the actuator. As the control element is biased towardsthe position in which openings 38 are covered, it is a normally closedelement. As discussed later in conjunction with the description of theembodiment of the control element shown in FIGS. 4 and 5, otherembodiments of the expansion valve of the present invention may havenormally open control elements.

When movable member 42 is moved in a direction downward as shown inFIGS. 2 and 3, peripheral surface 58 moves to uncover openings 38 instem member 28. As a result, the area outside the control element inchamber 18 is in fluid communication with internal passage 30 of thecontrol element, and outlet 16 of the valve, through ducts 40. Theextent to which openings 38 are uncovered determines the flow rate ofrefrigerant material through the control element, and thus the flow ratefrom the inlet to the outlet of the expansion valve.

The proportional solenoid 22 of the expansion valve is shown in greaterdetail in FIG. 6. The proportional solenoid 22 includes an isolationtube 62. Isolation tube 62 is generally cylindrical and has a closed top64. Isolation tube 64 also has a flanged bottom 66 which nests in arecess (not separately shown) in body 12. In the preferred form of theinvention isolation tube 66 is made of non-magnetic stainless steelmaterial having approximately one-half inch O.D. and a 0.012 inch thickwall. The body 12 is preferably made of non-magnetic aluminum alloy.

A resilient seal 68 is positioned under flange bottom 66 of isolationtube 62. Seal 68 serves to provide a fluid tight seal which prevents theworking fluid in chamber 18 from escaping around the isolation tubethrough the recess. The isolation tube is fixed in position as shown byfastening means (not shown). A flux washer 69 made of magnetic materialis positioned in the recess above flange bottom 66 of the isolationtube. The preferred form of the flux washer is sized with an openingthat accepts the isolation tube, has a one inch O.D. and is 0.180 inchesthick. The purpose of flux washer 69 is later described in detail.

The isolation tube 62 has a cylindrical surface 70. Plunger 24 ismovable inside an internal area 72 of the isolation tube. Internal area72 is bounded by interior surface 70. As described in co-pending patentapplication Ser. No. 07/951,259, now U.S. Pat. No. 5,252,939, plunger 24includes rollable bodies 74 that roll between the surface of plunger andthe interior surface 70 of the isolation tube. Further, the isolationtube provides a radial gap in which there is no magnetic materialbetween the plunger and the lower portion of the frame. This radial gapis approximately 0.20 inches. This construction enables plunger 24 tomove with virtually no frictional resistance.

Proportional solenoid 22 further includes a wound wire coil 76 forproviding an electromagnetic field when electrical power is suppliedthereto. Coil 76 is supported in a frame 78 made of magnetic materialthat is u-shaped in cross section. A cylindrical sleeve 80 extends partway through the center of coil 76. A longitudinal gap 82 extends betweenthe bottom of sleeve 80 and the lower portion of frame 78 as shown inFIG. 6. In the preferred embodiment the length of this longitudinal gapis 0.300.

In the preferred embodiment of the invention the inside diameter ofsleeve 80 is slightly larger than the outside diameter of isolation tube62. In addition, in the preferred embodiment, frame 78 may be releasablyattached to body 12 of the valve. This enables the coil and frameassembly to be removed from the valve without releasing any of therefrigerant working fluid 20 from the system. This makes it easier torepair or replace the coil of the solenoid actuator.

An operation of the expansion valve, when no electrical power is appliedto coil 76, the spring 48 of control element 20 biases plunger 24 upwardto the position shown in FIGS. 1 and 6. Supplying power to coil 76creates an electromagnetic field. The electromagnetic field produces aflux circuit about solenoid 22. The flux circuit extends through thesleeve 80, the frame 78 and the flux washer 69. However, gap 82 causesmagnetic saturation in the area of the gap.

The plunger functions as a member for completing the magnetic fluxcircuit. Flux washer 69 serves as a variable permeance element as itspermeance varies with the distance the plunger 24 is displaced downward.As electrical power delivered to the coil of the solenoid actuatorincreases, the magnetic saturation at the gap 82 also increases. Thiscauses the plunger to move downward until the force reaches anequilibrium with the biasing force of the spring of the control element.

By varying the amount of power delivered to the coil of the proportionalsolenoid, the position of the plunger and the movable member 42 of thecontrol element may be precisely controlled. As a result, the rate offlow of working fluid through the valve is also accurately regulated.

The proportional solenoid of the present invention is novel in thatunlike conventional solenoids the force it produces does not increaseexponentially as the plunger approaches the end of its stroke. Thisenables the solenoid actuator to achieve a force versus strokecharacteristic that enables precise and repeatable movement.

Solenoid 22 is further novel in that although it is a proportionalsolenoid, it is removable from the body of the valve. This facilitatesrepair or replacement. Prior art type proportional solenoids have notgenerally been used in expansion valves because they could not toleratea low permeance structure between the coil sleeve and the plunger. Inthe present invention however, a low permeance non-magnetic isolationtube is positioned between the magnetic sleeve and the plunger element.The presence of this low permeance tube actually enhances the ability ofthe plunger to move. This is believed to occur because the low permeanceelement maintains the plunger away from other magnetic elements andreduces resistance to movement that occurs when a magnetic element thatis attracted to the plunger is immediately adjacent thereto.

It will be understood by those skilled in the art, that although thepreferred embodiment of the invention uses an air gap to achieve asaturation area, in other embodiments a non-magnetic spacer or thinnedarea of the sleeve may be used. Likewise, although the preferredembodiment includes a flux washer as a variable permeance element, otherembodiments may use other types of elements that exhibit increasingpermeance with plunger stroke.

In operation of the proportional solenoid, as greater electrical poweris delivered to coil 76 plunger 24 moves in a downward direction asshown in FIG. 1. Because movable member 42 is engaged with plunger 24,it likewise moves downward. This opens flow through openings 38 in theouter surface of the stem member 28. As a result, working fluid on theoutside of the control element in chamber 28 flows through the controlelement and into the internal passage of the stem member. Becauseopenings 38 are elongated, the further the movable member moves downwardthe greater the flow through the control element.

The configuration of the control element enables precise control of theflow therethrough in response to the displacement of the movable member.In addition, because the movement of the movable member to open andclose the control element is perpendicular to the direction of fluidflow, the fluid acts equally on all surfaces of the movable member. Thisavoids the creation of any significant forces due to flow effects.Further, the taper of peripheral surface 58 of the movable member avoidsflow and pressure effects that would tend to resist movement of themovable member.

The control element provides precise and predictable flow control inresponse to the power delivered to the proportional solenoid. As aresult, the expansion valve of the present invention may be used toachieve more accurate control of the cooling characteristics when usedin an air conditioning or other heat transfer system.

A typical system in which the expansion valve 10 of the presentinvention may be used is shown schematically in FIG. 7. Liquid workingfluid enters inlet 14 of the expansion valve. The expanded refrigerantleaves the outlet 16 and is delivered in a suitable conduit to anevaporator 84. The working fluid absorbs heat as indicated by the arrowslabeled Q-in, as the working fluid flows through the evaporator. Ofcourse in the preferred form of the invention, which is an airconditioning system for a vehicle, the evaporator is in the passengercompartment or other area to be cooled. A fan 86 shown schematicallyreflects that air is drawn through the evaporator to assist in heattransfer.

Working fluid exiting the evaporator travels in a suitable conduit backthrough return passage 26 of valve 10. As previously discussed, thereturn passage through the valve provides a suitable location fortemperature and/or pressure sensors to detect the properties of therefrigerant vapor exiting the evaporator.

The vaporized working fluid is compressed by compressor 90 and deliveredin a suitable conduit to a condenser 92. In condenser 92 the workingfluid loses heat as reflected by the arrows labeled Q-out. In thecondenser 92 the working fluid condenses to a liquid. A fan 94 shownschematically aids in transferring heat from the working fluid as itpasses through the condenser. In the preferred embodiment of theinvention, which is an air conditioning system for a vehicle, heat istransferred from the working fluid to the environment.

From the condenser the liquefied working fluid is returned to the inlet14 of the expansion valve, after first passing through a receiver-drier88. Receiver-drier 88 serves to remove impurities, and suchreceiver-driers are well known to those skilled in the art.

The proportional solenoid 22 is actuated by an electronic control moduleshown schematically as 96. Control module 96 includes a processor andoperates to deliver signals to the solenoid to selectively control theflow rate of refrigerant through the expansion valve. The control moduleis further electrically connected to sensors (not shown) which detectthe characteristics of the working fluid as it leaves the evaporator,and perhaps other characteristics of the system, which enables thecontrol module to calculate the appropriate amount of working fluid thatshould optimally pass through the expansion valve and to convert thisamount into a signal. Those skilled in the art may devise numerous waysof sensing the parameters desired to be used to control the flow ratethrough the expansion valve and for the control module 96 to properlyactuate the valve to provide the desired flow.

While the preferred embodiment of the invention includes a proportionalsolenoid to move the control element which controls the rate of flowthrough the valve, in other embodiments other types of actuators may beused. Although such actuators may not provide as precise flow control asthe proportional solenoid of the preferred embodiment, the novel controlelement of the present invention may still be successfully used.

The embodiment of the valve shown in FIG. 1 includes a normally closedcontrol element 20. However other embodiments of the invention mayinclude control elements that are normally open. Such a normally openedcontrol element 98 is shown in FIGS. 4 and 5. Control element 98 isdesigned to be a direct replacement for control element 20, and element98 may be substituted in expansion valve 10 without changes to the valveconstruction. However the actuation of the proportional solenoid by thecontrol module would have to be changed to reflect the differentcharacter of the control element.

Control element 98 has a threaded lower portion 100 similar to threadedportion 32 of valve element 20. Also like the previously describedcontrol element, element 98 has a stem member 102 with an internalpassage 104. Control element 98 also has an external hex area 106 forease of attachment and removal.

Control element 98 further includes a cylindrical outer surface 108. Apair of openings 110 in surface 108 are connected through ducts 112 tointernal passage 104. Openings 110 are elongated longitudinally alongthe axis of the stem member as shown.

Control element 98 also includes a movable member 114. Movable member114 has a cylindrical inner surface 116 slightly larger in diameter thanouter surface 108. This enables the movable member to movelongitudinally on the outside of the stem member. The stem member 102also includes a plurality of ridges 118 in the area above openings 110as shown in FIG. 5.

Movable member 114 further includes a downwardly tapered peripheralsurface 120 which terminates at an edge 123 adjacent its lower end.Movable member 114 further includes a plunger engaging portion 124 forengaging plunger 24. A compression spring 126 biases the movable memberin the upward direction as shown in FIGS. 4 and 5. Stem member 102further includes a detent 128 for helping to center spring 126 inposition.

In operation of an expansion valve that includes control element 98,full flow is achieved when movable member 114 is disposed in its fullyupward position. This occurs when no power is delivered to theproportional solenoid and plunger 24 is disposed fully upward as shownin FIG. 1.

As electrical power to the coil of the solenoid is increased, theplunger moves downward and the movable member 114 moves similarlyagainst the force of spring 126. As the movable member partially coversopenings 110, flow through the control element is reduced. The flow iscontrolled by selectively moving the movable member to cover theopenings to the extent desired to achieve the appropriate flow rate.

Like control element 20, control element 98 is not significantlyinfluenced by forces generated by the flow of the refrigeranttherethrough. It also provides accurate and repeatable flow based on theposition of the movable member by the proportional solenoid.

A further advantage of the construction of the control elements of thepresent invention is that fluid may flow through the valve in eitherdirection. This avoids the need to connect the valve with particularports as the inlet and outlet. It is also useful in heat pumpapplications in which refrigerant flow is reversed.

In the preferred construction of control elements 20 and 98, a pair ofopposed fluid openings in the stem member are used. These openings areelongated to provide a wide range of flow rates. In other embodiments ofthe invention, other numbers of openings and other configurations ofopenings may be used depending on the range of flow rates desired.

It will be understood by those skilled in the art that although theproportional solenoid 22 of the expansion valve of the present inventionis adapted for controlling elements such as control elements 20 and 98,the proportional solenoid may also be used in other embodiments of theinvention to control other types of flow control elements.

Thus, the new expansion valve for an air conditioning system of thepresent invention achieves the above stated objectives, eliminatesdifficulties encountered in the use of prior devices and systems, solvesproblems and attains the desirable results described herein.

In the foregoing description certain terms have been used for brevity,clarity and understanding. However, no unnecessary limitations are to beimplied therefrom because such terms are for descriptive purposes andare intended to be broadly construed. Moreover, the descriptions andillustrations given are by way of examples and the invention is notlimited to the exact details shown or described.

Having described the features, discoveries and principles of theinvention, the manner in which it is constructed and utilized, and theadvantages and useful results obtained; the new and useful methods,structures, devices, elements, arrangements, parts, combinations,systems, equipment, operations and relationships are set forth in theappended claims.

We claim:
 1. A proportional solenoid comprising: a non-magneticisolation member having a closed first end and an open second end; amagnetic plunger disposed in said isolation member, said plunger beinglongitudinally movable within said isolation member between said firstand second ends; a magnetic frame means that supports a coil connectableto an electrical supply; said frame means supporting said coil on amagnetic sleeve; said frame means having an opening at one end thereofand being adapted to receive said isolation member through said openingso that said frame means and coil can be removed from said isolationmember and plunger; flux saturation means disposed longitudinallybetween one end of said plunger and one end of said sleeve for providingan area of magnetic flux saturation through said plunger; wherein saidflux saturation means comprises a longitudinal air gap between and boundby said sleeve one end and said frame means one end; and a variablepermeance element disposed adjacent said flux saturation means andaxially adjacent said plunger one end; said variable permeance elementand plunger coacting to produce an area of variable permeance inrelation to position of said plunger within said isolation member. 2.The apparatus of claim 1 wherein said variable permeance elementcomprises a flux washer disposed adjacent said frame means at saidopening.
 3. The solenoid of claim 1 wherein said plunger comprises anumber of rollable bodies in contact with said isolation member toprovide low friction movement of said plunger within said isolationmember.
 4. The solenoid of claim 1 wherein said isolation member extendslongitudinally from a second end of said frame means opposite said framemeans one end through said opening to a length at least past saidvariable permeance element.
 5. The solenoid of claim 1 wherein saidvariable permeance element is adapted to secure said isolation memberopen end to a valve body so that said plunger can engage a valve controlelement.
 6. A proportional solenoid comprising: a non-magnetic isolationmember having a closed first end and an open second end; a magneticplunger disposed in said isolation member, said plunger beinglongitudinally movable within said isolation member between said firstand second ends; a magnetic frame that supports a coil connectable to anelectrical supply; said plunger comprising rollable bodies in contactwith said isolation member with said isolation member and rollablebodies cooperating to substantially reduce hysteresis in plungermovement in relation to current in said coil by reducing radial forcesacting on said plunger; said frame supporting said coil on a magneticsleeve; said frame having an opening at one end thereof and beingadapted to receive said isolation member through said opening so thatsaid frame and coil can be removed from said isolation member andplunger; a flux saturation element disposed longitudinally between oneend of said plunger and one end of said sleeve for providing an area ofmagnetic flux saturation through said plunger; and a variable permeanceelement disposed adjacent said flux saturation element and axiallyadjacent said plunger one end; said variable permeance element andplunger coacting to produce an area of variable permeance in relation toposition of said plunger within said isolation member.
 7. A solenoidcomprising:an actuator member comprised of magnetic material; anisolation member comprised of nonmagnetic material, said isolationmember having an interior area, said actuator member movablelongitudinally in said interior area; a sleeve member comprised ofmagnetic material, said sleeve member in surrounding relation of saidisolation member, said sleeve member terminating at a longitudinal edgesurface; a longitudinal non-magnetic gap adjacent said sleeve memberedge surface; a variable permeance element longitudinally disposed fromsaid edge surface of said sleeve member, said variable permeance elementincluding means for accepting said actuating member adjacent thereto invariable longitudinal position; an electrical coil in generallysurrounding relation of said sleeve member, said coil having a first endand a second end; and a frame comprised of magnetic material supportingsaid coil, said frame extending adjacent said sleeve member at saidfirst coil end and adjacent said variable permeance element at saidsecond coil end, and wherein said nonmagnetic gap is bound by saidsleeve member edge surface and said frame.
 8. The solenoid according toclaim 7 wherein said variable permeance element includes an opening, andwherein said actuating member is movable into said opening.
 9. Thesolenoid according to claim 7 wherein said sleeve member islongitudinally movable on said isolation member.
 10. The solenoidaccording to claim 8 wherein said isolation member and said interiorarea thereof extend longitudinally thorough said opening in saidvariable permeance element.
 11. The solenoid according to claim 7wherein said actuator member moves longitudinally in a direction ofincreasing permeance when current is conducted by said coil.
 12. Thesolenoid of claim 11 wherein when said coil is energized with a current,the solenoid operates with proportional movement in relation to coilcurrent magnitude.
 13. The solenoid of claim 11 wherein said actuatormember, frame, variable permeance element and coil provide a magneticflux path for inducing movement of said actuator member withoutlongitudinally contacting a magnetic pole piece.